The present invention relates to apparatus and methods for conversion of signals between those transmitted over bimetallic cables and those transmitted over fiber optic cables.
The use of fiber optics in the cable segment that links the equipment closest to the computer workstations for connection into a Local Area Network (LAN) has been inhibited by the relatively high cost associated with the support electronics and by technology limitations. However, this workstation to closet cable segment, normally referred to as the "horizontal segment", represents a large market because of the large number of such installations.
Recent developments in fiber optic technology have greatly reduced the cost of the support electronics for LAN devices. When this technology is viewed from the perspective of the large number of installations in which such fiber optic technology might be employed, the utilization of fiber optics in the horizontal segment becomes a cost effective reality for LAN applications.
IEEE Standard 802.3u, the governing standard for Fast Ethernet, currently defines the 100 Base-FX fiber optic standard for Fast Ethernet. This standard requires that the fiber optic devices operate at a wavelength of 1300 nm. Since Fast Ethernet requires up to 125 MHZ of bandwidth, the 1300 nm wavelength overcomes the bandwidth problems of 62.5/125 multi-mode fiber optic cable, and 100Base-FX links can operate over a distance of 2,000 meters.
If light of shorter wavelength (850 nm) could be employed effectively, it would enable a significant reduction in cost since light transmitters that generate light in the short wavelength region may be based on a light emitting diode (LED) and not a laser. This has a dramatic impact in the cost. Short wavelength receivers referred to as PINs, are also considerably lower in cost than those used in laser applications. However, short wavelength LEDs and PINs are now capable of bandwidth greater than 125 MHZ.
There are numerous LAN protocols in use today but the focus of the present invention is upon the physical connection for Fast Ethernet over multi-mode fiber using short wavelength light. At present there is no standard that defines the use of short wavelength light as a carrier wave for Fast Ethernet (i.e., 100 Mbs) data over 62.5/125 multi-mode fiber optic cable. Short wavelength generally refers to light in the 850 nanometer (nm) wavelength region.
The technical advantage of using longer wavelength light for Fast Ethernet is apparent based upon the following comparison:
Wavelength 850 nm 1300 nm Ratio 160 MHZ/km.sup.1 400 MHZ/km
However, in evaluating short versus long wavelengths, two main factors should be considered:
1. LEDs and PINs designed for 1300 nm operation require a semiconductor substrate different from what is used for 850 nm devices. The difference in substrate, along with low yield rates, results in a high cost making the use of 1300 nm devices with lasers cost prohibitive. PA1 2. Approximately 95% of all horizontal applications use a cable segment that is less than 500 meters. This distance is well within the operational envelope of short wavelength devices and bandwidth of multi-mode fiber.
Accordingly, it is an object of the present invention to provide a novel media converter including an LED to produce the light pulses for fiber optic transmission in a local area network.
It is also an object to provide such a media converter which is relatively economical to fabricate and which is relatively trouble free in operation.
Another object is to provide such a media converter which is easily adapted to operate at either 850 nm or 1250 nm.
A further object is to provide a novel method for effecting media conversion in a device using fiber optics and an LED.